Preliminary trial results for encroacher and invasive biomass based torrefied wood chips as household fuel: Feedstocks from South Africa, Namibia and Botswana

Abstract

The performance of torrefied wood chips when used as a household fuel has been evaluated in comparison to that of raw wood chips, firewood, briquettes and charcoal. The torrefied wood chips were produced from a superheated steam technology using encroacher and invasive bushes found in Southern Africa. Laboratory tests included measurement of the physicochemical characteristics and water boiling tests of the fuels. Field trials were conducted within communities of Namibia and Botswana that were involved in cooking and barbeque activities. Charcoal had the highest calorific value of 23.71 MJ/kg and it also displayed the best fire holding capacity. Although torrefied wood chips had the second highest calorific value of 18.73 MJ/kg, its fire holding capacity was the poorest among the tested fuels as it burned quite fast and vigorously. Charcoal also outperformed all the tested solid fuels in terms of thermal efficiency of 26%. The lowest efficiency was recorded on raw wood chips at 19.5%. Briquettes and torrefied chips stood at 25% and 20% thermal efficiency, respectively. Field measurements of cooking times, amount of food cooked and frequency of fuel feeding into the stove corroborated with laboratory-based results. Overall, the torrefied wood chips demonstrated potential use as firelighters and there is scope to technically improve the attributes of the chips so that they can compete with traditional fuels in terms of cost and accessibility to consumers. There is great potential for encroacher and invasive biomass valorization through torrefaction to produce solid fuel in Southern Africa towards the fulfilment of several sustainable development goals through this initiative.